What is milk thistle?
Milk thistle is a plant that contains silymarin, a substance that improves liver function. Originally from Europe, milk thistle now also grows in the United States.
You can take milk thistle in capsules or as a tincture (combined with alcohol). It has been widely used in Europe and Germany, where it is a common complementary treatment for liver problems such as hepatitis and cirrhosis. In the United States, it is sold as a dietary supplement.
What is milk thistle used for?
People use milk thistle as a complementary treatment for liver problems, particularly hepatitis and cirrhosis and inflammation of the bile ducts (cholangitis). Research on silymarin suggests that it may protect the liver from inflammation. But it does not have a direct effect on viruses that cause hepatitis, such as the hepatitis C virus.footnote 1
Preliminary research suggests that silymarin is an antioxidant, which helps protect the body from cell-destroying substances called free radicals. Silymarin also may reduce inflammation and block the effects of toxins that harm the liver.footnote 2
Two studies on milk thistle presented conflicting results. One study found that milk thistle appeared to help some people with cirrhosis live longer than they would have otherwise, while another found no benefit.footnote 2
Is milk thistle safe?
Milk thistle may cause nausea, diarrhea, bloating, pain, or allergies.
The U.S. Food and Drug Administration (FDA) does not regulate dietary supplements in the same way it regulates medicines. A dietary supplement can be sold with limited or no research on how well it works.
Always tell your doctor if you are using a dietary supplement or if you are thinking about combining a dietary supplement with your conventional medical treatment. It may not be safe to forgo your conventional medical treatment and rely only on a dietary supplement. This is especially important for women who are pregnant or breastfeeding.
When using dietary supplements, keep in mind the following:
- Like conventional medicines, dietary supplements may cause side effects, trigger allergic reactions, or interact with prescription and nonprescription medicines or other supplements you might be taking. A side effect or interaction with another medicine or supplement may make other health conditions worse.
- Dietary supplements may not be standardized in their manufacturing. This means that how well they work or any side effects they cause may differ among brands or even within different lots of the same brand. The form you buy in health food or grocery stores may not be the same as the form used in research.
- Other than in vitamins and minerals, the long-term effects of most dietary supplements are not known.
- National Center for Complementary and Alternative Medicine (2012). Get the facts. Hepatitis C: A focus on dietary supplements. (NCCAM Publication No. D422). Available online: http://nccam.nih.gov/health/hepatitisc/hepatitiscfacts.htm?nav=gsa.
- Murray MT (2013). Silybum marianum (milk thistle). In JE Pizzorno, MT Murray, eds., Textbook of Natural Medicine, 4th ed., pp. 1026–1031. St. Louis: Mosby.
Other Works Consulted
- Milk thistle (2010). In A DerMarderosian et al., eds., Review of Natural Products. St. Louis: Wolters Kluwer Health.
Current as of: April 9, 2019
Author: Healthwise Staff
Medical Review: Adam Husney, MD - Family Medicine
Current as of: April 9, 2019